This invention relates to a suspension system for a vehicle having a suspension arm member whose inner end is supported, at two points spaced apart in longitudinal direction of the vehicle body, to a vehicle body member and an assist link fixed thereto. This invention is particularly intended for coexistence of comfortableness to ride in and driving stability.
The Japanese Utility Model Registration Application Laying Open Gazette No. 64-49404, for example, discloses a suspension system of this kind. This suspension system comprises a suspension arm member whose inner end is supported swingably, at two points spaced apart in longitudinal direction of the vehicle body, to a vehicle body member and whose outer end is supported swingably to a wheel support member and an assist link, extending in right and left direction of the vehicle body, whose outer end is supported swingably to an intermediate part of the suspension arm member and whose inner end is supported swingably to a vehicle body member which is on an axial center of the vehicle body side parts are supported elastically to the vehicle body member through the medium of bushes or the like.
In the above case, provision of the assist link extending in right and left direction of the vehicle body heightens effectively the lateral rigidity of the suspension arm member which resists external force from the right and left direction of the vehicle body at turning of the vehicle boyd, for example, and thus driving stability at turning is improved. Provision of the assist link also makes it possible to soften the bush of one of the vehicle body side support parts (vehicle body side support part close to the assist link), whereby input from longitudinal direction of the vehicle body which acts when a vehicle runs over roughness of the road, for example, is let escape by moving the wheel positively in front and rear direction and as a result, compliance in front and rear direction is ensured and comfortableness to ride in is improved.
Recently, it has been demanded to make the comfortableness to ride in (when a vehicle runs over roughness of the road, for example) and the driving stability at turning coexist at a high level by ensuring fully compliance in front and rear direction when a vehicle runs over roughness of the road, for example, and input from the longitudinal direction of vehicle body acts, by lowering rigidity in front and rear direction at the vehicle body side support part of the suspension arm member while lateral rigidity of the suspension arm member is in heightened state.
In the above case, however, since the vehicle body side support part of the suspension arm member is supported to the vehicle body member through the medium of a bush or the like, rigidity against input from longitudinal direction of the vehicle body at the vehicle body side support part of the suspension arm member is high. Therefore, even if a bush close to the assist link (out of bushes of two vehicle body side support parts) is made soft, quantity of moving the wheel in front and rear direction against input from longitudinal direction of the vehicle body when a vehicle runs over roughness of the road, for example, becomes very small. Therefore, there is a limit in ensuring compliance when input from longitudinal direction of a vehicle body acts by softness of a bush close to the assist link while securing rigidity against input from lateral direction of the vehicle body at turning, for example, only by the assist link and it is impossible to make the comfortableness to ride in (when a vehicle runs over roughness of the road, for example) and the driving stability at turning coexist.